Lots of discussions on US + UK vehicles forums and vintage machinery forums (
https://www.google.com.au/search?sou...sclient=psy-ab) list the history of this oil and possible modern equivalents.
Suggestions include 140W Gear Oil, 250W Gear Oil or 680 Steam Oil.
Some even consider that the "W" does not refer to Weight or Winter as per modern parlance, but that the original oil was Mineral Oil compounded with Whale Oil! Try finding that today.